The present invention relates to baluns and in particular to baluns adapted to electrically connect a twisted pair cable to a coaxial cable. The invention further relates to a method for connecting a twisted pair cable to a coaxial cable.
Baluns, or impedance matching devices as they are also known, are used to connect cables having differing impedances. For example, a common requirement in the telecommunications industry is the connection of twisted pair cabling, typically having an impedance of 120 ohms, with coaxial cables which usually have an impedance of 75 ohms and similar impedance matching to systems.
Known baluns can potentially degrade the overall performance of cabling by allowing either internal electromagnetic radiation to escape from the cable or external electromagnetic radiation to interfere with the signals conveyed thereon. In addition, some known baluns require the use of specialised tools to complete the connection process. Further, known baluns are bulky thereby wasting valuable space, particularly, for example, in large telecommunications stations where thousands of baluns may be connected in parallel and in close proximity. Known baluns also do not provide a rigid connection, thereby potentially exposing components and connections to bending stresses and the like.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
According to a first aspect of the invention there is provided a balun adapted to electrically connect a twisted pair cable to a coaxial cable, said twisted pair cable having two active wires, an earthing wire and shielding, said balun including:
a hollow conductive cover defining first and second apertures; said first aperture being sized to accept said twisted pair cable; said cover, when in use, housing an earthing means for electrically connecting said earthing wire and/or shielding to said cover; said cover, when in use, further housing first mounting means adapted to mount said active wires in close proximity to said second aperture; and
a body housing second mounting means adapted to mount a pair of first connectors projecting from said body; said body further housing a first transformer electrically connected to said first connectors; an end of said body defining a coaxial connector being electrically connected to said first transformer,
whereby said cover is mountable to said body such that an earthing connection is made therebetween, and such that said first connectors respectively electrically connect with said active wires, thereby completing an impedance matching electrical circuit between said twisted pair cable and said coaxial cable connector.
Preferably the earthing means is a metallic ring around which said shielding is wrappable and to which said earthing wire is connectable. The cover preferably includes a first cylindrical portion of minor diameter defining said first aperture and a second cylindrical portion of major diameter defining said second aperture, said first and second portions being joined by a radial portion, said ring being adapted to abut said radial portion within said second cylindrical portion.
According to a second aspect of the invention there is provided a method for connecting a twisted pair cable having two active wires, an earthing wire, shielding and outer insulation to a coaxial cable, said method including the steps of:
i) threading said twisted pair cable through a hollow conductive cover;
ii) removing a length of outer insulation from the twisted pair cable;
iii) connecting said shielding and/or said earthing wire to an earthing means;
iv) mounting, said active wires in a first mounting means;
v) housing said first mounting means in said cover such that said earthing means and associated shielding and/or earthing wire make earthing contact with said cover and such that said active wires are disposed adjacent an aperture of said cover;
vi) mating a body with said cover such that first connectors projecting from said body make electrical connection with said active wires, said body including a first transformer electrically connected to said first connectors, said body further including a coaxial connector electrically connected to said first transformer; and
vii) connecting said coaxial cable to said coaxial connector.
It will be appreciated that while the invention has been described above with reference to connection of cables, it can also be used to connect either a twisted pair or a coaxial cable directly onto a system. For example the connection of a twisted pair cable onto a coaxial connector disposed on a piece of telecommunications hardware.